Cracking reaction product characteristics

Decomposition of methoxynaphthalene In supercritical water at 390 C occurs by proton-catalyzed hydrolysis and results In 2-naphthol and methanol as main reaction products. The rate of hydrolysis Is enhanced by dissolved NaCl. The dielectric constant and the Ionic strength of supercritical water was found to affect the hydrolysis rate constant according to the "secondary salt effect rate law, which commonly describes Ionic reactions In liquid solvents. In subcrltlcal water vapor the decomposition of the ether results In a mixture of cracking products and polycondensates, which Is characteristic for a radical type thermolysis. 

As was the case of n-dodecane cracking, the catalytic activity was the highest for the hybrid catalyst under hydrogen pressure. The characteristic feature of the product distribution is tliat the reaction products of H2-hybrid catalyst system are only isomerized heptane and propane and equimolar amount of isobulane (little n-C4Hio was formed), whereas the products on H-ZSM-5 alone distributed from C3 to C9 and C4 products contained all kind of pararfins and olefins. 

The complex then splits beta to the point of complexing to produce an olefin and a new hydrogen deficient entity. However, superimposed on this basic cracking reaction are the simultaneous and consecutive reactions which produce the characteristic catalytic cracking product distribution. The relative stability of carbonium ions is tertiary > secondary > primary. There is, then, either a preferential formation of tertiary and secondary ions, or else isomerization to these preferred forms. The property of beta fission results in the formation from secondary ions of no olefins smaller than propylene, and from tertiary ions of no olefins smaller than isobutylene. Cycli-zation and hydrogen transfer reactions result in the large amounts of aromatic hydrocarbon formed. The sum total of these described reactions lead to the desirable product distribution characteristic of catalytic cracking. 

Hydrotreating of feeds intended for further processing is desirable to the extent that the principal contributors to poor product quality or refining characteristics are eliminated this assures protection of the expensive catalysts employed in reforming and cracking reactions. Undesirable effects produced by certain types of contaminates are itemized below ... 

Due to the retractive forces in stretched mbber, the aldehyde and zwitterion fragments are separated at the molecular-relaxation rate. Therefore, the ozonides and peroxides form at sites remote from the initial cleavage, and underlying mbber chains are exposed to ozone. These unstable ozonides and polymeric peroxides cleave to a variety of oxygenated products, such as acids, esters, ketones, and aldehydes, and also expose new mbber chains to the effects of ozone. The net result is that when mbber chains are cleaved, they retract in the direction of the stress and expose underlying unsaturation. Continuation of this process results in the formation of the characteristic ozone cracks. It should be noted that in the case of butadiene mbbers a small amount of cross-linking occurs during ozonation. This is considered to be due to the reaction between the biradical of the carbonyl oxide and the double bonds of the butadiene mbber [47]. 

Fundamental studies of catalytic cracking have led to the conclusion that the chief characteristics of the products may be traced to the primary cracking of the hydrocarbons in the feed stock and to the secondary reactions of the olefins produced both correspond to the ionic reaction mechanisms of hydrocarbons in the presence of acidic catalysts. The chemistry of both the hydrocarbons and catalysts dealt with here has advanced rapidly in the last decade. Nevertheless, much further exploration is required with respect to the nature of the catalyst and the properties of the hydrocarbons undergoing reaction. A promising field lies ahead for future research. 

The relative reactivity of hexane and 3-methylpentane (about 1000) in the isomerization mode was shown to be the same as found for isomerization in HF-SbF5.102 In the cracking mode, however, the ratio is about 10, resulting from the dramatic acceleration of the reaction of hexane compared to that of 3-methylpentane. Further characteristics of the cracking mode are a large excess of branched isomers in the C4—C5 fractions, the absence of unsaturated cracking products, and formation of... 

Depending on the plastic to be cast, solidification takes place at either room temperature or elevated temperatures. With room temperature systems chemical reaction occurs with the liberation of heat. The rate of heat dissipation can influence the performance and aesthetic characteristics of the hardened product. In thin sections, where a large area in relation to the total volume of the plastic is exposed, the heat of the exothermic reaction is dissipated rapidly and the temperature of casting is not very high. Thin sections can be cast at room temperature with no danger of cracking. When the rate of heat is excessive, application of heat may be necessary to properly control cure rate. 

Dealuminated Y zeolites which have been prepared by hydrothermal and chemical treatments show differences in catalytic performance when tested fresh however, these differences disappear after the zeolites have been steamed. The catalytic behavior of fresh and steamed zeolites is directly related to zeolite structural and chemical characteristics. Such characteristics determine the strength and density of acid sites for catalytic cracking. Dealuminated zeolites were characterized using X-ray diffraction, porosimetry, solid-state NMR and elemental analysis. Hexadecane cracking was used as a probe reaction to determine catalytic properties. Cracking activity was found to be proportional to total aluminum content in the zeolite. Product selectivity was dependent on unit cell size, presence of extraframework alumina and spatial distribution of active sites. The results from this study elucidate the role that zeolite structure plays in determining catalytic performance. 

In the process of catalytic cracking, characteristic reactions such as chain scission, hydrogen transfer and condensation take place under certain temperature and pressure conditions and when an appropriate catalyst is utilized, products with certain range of molecular weights and structures are obtained. Catalysts with surface acid sites and with the ability of hydrogen ion donation such as silica-alumina and molecular sieve catalyst have been already widely utilized. These catalysts can also enhance the isomerization of products and increase the yield of isomeric hydrocarbons. However, large amounts of coke will deposit on the surface of catalysts and consequently lead to their deactivation. Therefore, the recycling of catalysts is difficult to achieve. 

ABSTRACT As a step in the application of the cracking of tar in fuel gas amelioration the characteristics of the endothermic reaction potential of tar was studied experimentally and theoretically. In this context, however, due to the structural complexity of tar and/or tany constituents in fuel gas well defined hydrocarbons as tar model compounds were applied with inexpensive and readily available materials (dolomites, dolomitic magnesium oxide [MgO], quicklime [CaO]). The effects of operation condition on extent of hydrocarbon conversion, gas product composition, and corresponding endotherai of the reaction potential have been explored. The results obtained in this work provide a basis for ture considerations of catalytic tar cracking. 

---